This invention relates to certain indole derivatives, specifically, to certain 3-(imidazol-1-ylalkyl)indoles, and to their use in selectively inhibiting the action of the thromboxane synthetase enzyme, i.e., without significantly inhibiting the action of the prostacyclin synthetase or cyclo-oxygenase enzymes. The compounds are therefore useful, for example, in the treatment of ischaemic heart disease, stroke, transient ischaemic attack and migraine.